Recording information on a layer of orthoferrite with an electron beam

ABSTRACT

Recording information on a layer of orthoferrite by exposing the layer to an electron beam. The electron beam alters the electrical conductivity of the layer wherever it impinges. Information can be retrieved by scanning with an electron beam to detect the variations in conductivity.

United States Patent Ingrey 1 0ct.24, 1972 [54] RECORDING INFORMATION ON A [56] References Cited ggg ef za fi WITH AN UNITED STATES PATENTS 3,599,181 8/1971 Dearnaley ..340/l73 CR [72] Invent g z f z lz h Ottawa 3,182,299 5/1965 Weidman "346/74 CR [73] Assignee: Northern Electric Company Limited, Primary Examiner-Bernard KOniCk Montreal, Quebec, Canada Assistant Examiner-Stuart Hecker Filed: Feb 1971 Attorney-John E. Mowle 21 Appl. No.: 111,312 1 ABSTRACT Recording information on a layer of orthoferrite by [52] us CR 250/495 R 340/173 R exposing the layer to an electron beam. The electron 340/174 TF 340/174 346/74 beam alters the electrical conductivity of the layer [51] Int Cl Guc "/14 1c 13/00 'Gold 15/34 wherever it impinges. information can be retrieved by [58] i 340/373 CR 174TF 174 YC scanning with an electron beam to detect the varia- 340/173 R; 346/74 CR; 250/495 R tions in conductivity.

7 Claims, 1 Drawing Figure mtminwmn 3.101.115

INVENTOR SIDNEY l. J. INGREY BY Q PATENT AGENT 1 RECORDING INFORMATION ON A LAYER OF ORTI-IOFERRITE WITH AN ELECTRON BEAM This invention relates to the recording of information, particularly but not exclusively in recording as used for a memory system for the storage and retrieval of information, for example, for computer applications.

In particular the invention relates to the recording of information by the modification of the character of a material. Particularly the character of the layer of an orthoferrite is modified, or altered in a manner which will provide a substantially permanent record.

Short term modification of a material by high energy electrons is known, andused, but the modification is of short duration, often of a fraction of a second, and the irradiating time long, sometimes as much as seconds. In the present invention, the modification is of long duration, at least several weeks, and the information is recorded very rapidly, i.e. a fraction of a second.

Briefly, the invention provides a method of recording and storing, information on a layer of orthoferrite by exposing the layer to an energy source, which source produces a change, or modification, in the electrical characteristics of the layer.

The invention will be readily understood by the following description of a particular embodiment, by way of example only, inconjunction with the accompanying drawing which is a schematic illustration of one method of recording and retrieving information.

As illustrated in the drawing, information is written on a platelet 10 of ytterbium orthoferrites, by means of an electron beam 11 of approximately 1,000 A diameter. An electron gun 12 produces the electron beam,

which is accelerated through a potential of l to SOKV.

An on-off control 13 and a magnetic focusing lens 14 are provided. The deflection of the beam 11 is controlled by electrostatic X,Y controls 15.

By the use of the X,Y controls the beam 11 is moved over the platelet 10 to write information on the platelet. This can be in a continuous form, for example in the form of a square or sinusoidal wave form, or by use of the on-off control 13, a series of discrete items of information can be written.

The action of the electron beam on the platelet is not fully understood but a variation in resistance of the material of the platelet occurs at the position or positions on which the electron beam impinges. For a platelet of ytterbium an increased conductivity of electrons occurs. However for a CaO doped ytterbium crystal the reverse effect occurred, i.e. an increased resistance to electron flow.

The information is retrieved by the use of an electron beam. Thus as seen in the drawing, with the beam 11 operative, either the beam 11 can be used to scan the platelet 10 by operation of the X,Y controls 15, or the beam 11 can be maintained stationery and the platelet moved. In either method, the variation of current passing through the platelet is used to modulate a CRT display via a contact 16 and preamplifier 17 provided before the CRT 16. It can also be arranged that the output from the preamplifier 17 can be switched to a pulse meter via a contact 18. The beam current has two main components after hitting the crystal, the current I,

which is conducted through the specimen and the current 1 of back scattered electrons. Secondary electrons are also produced. In the example described, the

current I, has a value of 0.2 p.A, and is directly proportional to the electronic conductivity of the material.

The platelet 10 is mounted on a conducting support. The platelet 10 canbe in the form of a thin slice of material, but it is also possible to form a layer of suitable material on a conducting base, as for example by sputtering.

The writing of the information is instantaneous and permanent. Information written on a crystal was retrieved after 40 days. However, the information can readily be erased, if required, for example by heating for a few seconds at approximately 600 C. The material can then be reused. As stated above, the action of the electron beam on the material is not fully understood, but it is thought that there may be a change in the Fe""/l=e ratio in the material.

While the invention has been described with the information being'written by means of an electron beam, it is envisaged that other methods may be used, for example a laser beam.

Other methods of erasing can also be used. Thus, for example, whole, or part, of the information written on the surface can be erased by irradiating by a beam of reversed polarity to that of the writing beam. To be of use as a memory device, it is necessary that some suitable form of datum indication, either mechanical or electrical for example, be impressed on the surface or support, to enable the reading or retrieval means to be correctly aligned. Given such datum indication, any particular locality on the surface can be exposed to an energy source which has the reverse effect on the surface material to that of the original writing or recording source. The second exposure imposes change in characteristic of i the material which is of opposite polarity to that of the original change resulting in erasure of the information if the opposed polarities are of equal value. It can be seen that two consecutive'exposures would first erasethe original information, and then write new information in a reversed polarity. Such a method of erasure is likely to be of more use than heating, as localized erasure can be obtained, whereas heating will normally erase all the information on the surface.

It is possible to use beams of a smaller diameter than that given above. The smaller the beam diameter the more information that can be applied to a given area. Thus, for example, if 200 300A diameter electron beam is used, more than 10 pieces of information could be stored in a 1cm area.

The invention is applicable to the field of communications and particularly of the storage and retrieval of information for computer operations. Thus the output when a layer is scanned, instead of being applied to a CRT display, as described above, can be fed to a computer.

Thus, the invention provides a means for storing, and retrieving information rapidly, the information being permanently recorded in a very compact form.

What is claimed is: v

1. A method of recording information on a layer of orthoferrite comprising: mounting said layer in opposition to a source of an electron beam; exposing said layer to the electron beam; and moving the beam in a predetermined pattern relative to the layer to expose selected areas to said beam to produce a change in electrical conductivity in said layer in said selected areas.

2. A method as claimed in claim 1 wherein the beam is maintained at a constant energy level to record continuously on the layer.

3. A method as claimed in claim 1 wherein the beam energy level is varied between a maximum value and a minimum value to record information as a plurality of discrete items.

4. A method as claimed in claim 1 wherein the layer comprises a platelet attached to a conducting support. 

1. A method of recording information on a layer of orthoferrite comprising: mounting said layer in opposition to a source of an electron beam; exposing said layer to the electron beam; and moving the beam in a predetermined pattern relative to the layer to expose selected areas to said beam to produce a change in electrical conductivity in said layer in said selected areas.
 2. A method as claimed in claim 1 wherein the beam is maintained at a constant energy level to record continuously on the layer.
 3. A method as claimed in claim 1 wherein the beam energy level is varied between a maximum value and a minimum value to record informatioN as a plurality of discrete items.
 4. A method as claimed in claim 1 wherein the layer comprises a platelet attached to a conducting support.
 5. The method as claimed in claim 1 including the further steps of: scanning said layer with an electron beam; and sensing the variation in current passing through the layer to retrieve the information recorded on said layer.
 6. A method as claimed in claim 5 wherein the layer is formed on a conducting support.
 7. A method as claimed in claim 5 wherein the layer is scanned by moving the beam over the surface of the layer. 